1. Field of the Invention
The present invention relates to a method, a module, a device, a module and a system for detecting an environment noise by evaluating an infrasonic signal. Particularly, the method according to the present invention provides a continuous level adjustment algorithm to adapt the detection level to a noise background for evaluating the infrasonic signal, for example to monitor a certain ambiance or environment.
2. Description of the Prior Art
Sound frequencies in a frequency range of about 0.1 Hz up to 20 Hz are normally designated as infra-sound. Infra-sound or an infrasonic pulse is generated by small changes of the air pressure, respectively. Such small changes of the air pressure may be generated by opening or closing of a door or a window but even by persons moving though a room. Due to the object surfaces moving through the air small changes of the air pressure are released such that infrasonic pulses are emitted by the respective moving object. These infrasonic pluses or infra-sound may by detected in a radius of up to 50 m away from the emerging object. But the radius of detection is further dependent on background noise and the space within which the infra-sound is propagating.
To detect infra-sound special microphones are used. These microphones are adapted to detect low frequency sound since low frequency sound is additionally often of low amplitude or low power, respectively. Nevertheless, microphones able to detect infra-sound (about 0.1 Hz to 20 Hz) and speech (about 200 Hz to 15 kHz) are available at reliable detection sensitivity.
A couple of detector systems and devices are in use to protect environments, rooms, homes, buildings and cars from being accessed in an unauthorized way. The mainly used detectors are ultrasonic motion detectors, infra-red detectors, light barriers and the like. These detectors may be combined with an alarm system in order to secure a respective object. Also infra-sound detectors are able to monitor a space signalling an opening of a door or a window or even a motion within the monitored space. Such infra-sound detectors are well known and used in motor vehicles to trigger an alarm system for example to prevent burglary of the motor vehicles.
Applications are known where separate infra-sound detecting devices are connected to a mobile phone, like described in WO 99/53456. These infra-sound detecting devices are used to trigger or rise any kind of alarm or monitoring action.
Normally, special infra-sound detecting microphones are used for detecting infra-sound events. These infra-sound microphones are expensive and require the implementation of a separate infrasound microphone. The usage of microphones detecting sound in a wide frequency range covering infra-sound frequencies and voice/speech frequencies enables extending the devices processing voice/speech audio signals to an alarm system by operating these devices to evaluate infrasonic signals detected by the microphones.
Usually, infra-sound detection systems, especially used in combination with alarm systems, employ fixed detection levels. The detection level defines an infra-sound level, normally an infra-sound amplitude level, at which a detected infra-sound event is interpreted as event to be signalized for example by an alarm of the alarm system. The fixed detection level is often adjustable to the environmental noise background but the environmental noise background can change due to outer effects. For example, while monitoring the infra-sound within a motor vehicle, the monitored infra-sound background level is dependent upon the place where the motor vehicle is parked. Near a heavily used road the infra-sound background level may be higher than within a residential area. That means, that in case of a low detection level a lot of false alarms are triggered or in case of a high detection level a careful opening of a door might be unnoticed. Both cases are undesired.
The invention is a method for monitoring an environment by evaluating an infrasonic signal taking a sound of said environment.
The invention is a module of a surveillance system for monitoring the environment by evaluating an infrasonic signal.
The invention is a device of a surveillance system for monitoring by evaluating an infrasonic signal
The invention is a system of a surveillance system for monitoring by evaluating an infrasonic signal.
Therefore, a continuous level adjustment algorithm provides the possibility to pre-determine a detection level which is continuously adapted to the background level. The number of false alarm of an alarm system which uses this algorithm to evaluate measured infra-sound can be reduced while the overall sensitivity of the infra-sound event detection is quite low arid hence reliable.
According to a first aspect of the invention a method of a surveillance system for monitoring by evaluating an infrasonic signal is provided. An infrasonic signal is averaged to yield an averaged infrasonic signal. The averaged infrasonic signal is mapped according to a function to yield an infrasonic noise signal. This infrasonic noise signal is averaged to yield an averaged infrasonic noise signal. By offsetting the averaged infrasonic noise signal with an offset value an infrasonic level signal is provided. This infrasonic level signal is compared with the averaged infrasonic signal. According to the comparison if the averaged infrasonic signal is greater than the infrasonic level signal a trigger signal is generated.
The infrasonic signal may be provided by filtering. The filtering may be employed on signals comprising infrasonic signals and non-infrasonic signals, i.e. signals of non-infrasonic frequency. Hence, the characteristic of the filtering may be limited to an infrasonic frequency range. The filtering may be a band-pass filter employed to extract an infrasonic signal. The band-pass filter characteristic may be limited to an infrasonic frequency range. A low-pass filter may also be employed for extracting the infrasonic signal. Accordingly, the low-pass filter characteristic may be limited to an infrasonic frequency range.
The averaged infrasonic signal may be a root mean square infrasonic signal. But also further averaging methods may be employed on the infrasonic signal to yield the averaged infrasonic signal.
The mapping of the averaged infrasonic signal may also comprise an additional rating of the function result with the averaged infrasonic noise signal. The function for mapping may be a non-linear function. This function may be used for weighting an additional rating signal, especially the averaged infrasonic noise signal. The function argument may by the result of an arbitrary combination of the averaged infrasonic signal arid the averaged infrasonic noise signal. Particularly, the argument may be the result of the division of the averaged infrasonic signal and the averaged infrasonic noise signal. Moreover, the function may map the result the division of the averaged infrasonic signal and the averaged infrasonic noise signal to provide a function result and this function result may be multiplied with the averaged infrasonic noise signal to provide the infrasonic noise signal.
The offset value may be an absolute offset value, increasing the averaged infrasonic noise signal by a constant absolute value. The offset value may be a relative offset value. The increasing offset of the averaged infrasonic noise signal is determined relatively to the averaged infrasonic noise signal. Further, the offset value may be multiplied with the averaged infrasonic noise signal to provide the infrasonic level signal. Particularly, the offset value may be defined by a signal-to-noise ratio (SNR). Moreover, the offset value may be adjustable to adapt the evaluation method to different operating conditions.
According to another aspect of the invention a software tool of a surveillance system for monitoring by evaluating an infrasonic signal is provided. The software tool comprises program potions for carrying out the operations of the aforementioned methods of a surveillance system for monitoring by evaluating an infrasonic signal when the software tool is implemented in a computer program and/or executed on a computer, a processing device or a digital signal processing device.
According to another aspect of the invention a computer program product is provided which comprises program code portions stored on a computer readable medium for carrying out the aforementioned methods of a surveillance system for monitoring by evaluating an infrasonic signal when the program product is executed on a computer, a processing device or a digital signal processing device.
According to another aspect of the invention a module of a surveillance system for monitoring by evaluating an infrasonic signal is provided. The module comprises a first averaging component for averaging the signal to provide an averaged infrasonic signal, a mapping component for mapping the averaged infrasonic signal according to a function to provide an infrasonic noise signal, a second averaging component for averaging the infrasonic noise signal to provide an averaged infrasonic noise signal, an offsetting component for offsetting the averaged infrasonic noise signal with an offset value to provide an infrasonic level signal, a comparing component comparing the infrasonic level signal with the averaged infrasonic signal and a generating component generating a trigger signal if the averaged infrasonic signal is greater than the infrasonic level signal.
The module may also comprise a filter component for filtering the infrasonic signal. The filter component may be employed on signals comprising infrasonic signals and non-infrasonic signals, i.e. signals of non-infrasonic frequency. For filtering the infrasonic signal the filter component characteristic may be limited to an infrasonic frequency range. It may be possible to employ a band-pass filter or a low-pass filter on the infrasonic signal.
The averaging component may. be a root mean square averaging component to provide a root mean square infrasonic signal as averaged infrasonic signal.
The mapping of the averaged infrasonic signal may also comprise an additional rating of the function result with the averaged infrasonic noise signal. Therefore, the module may also comprise a rating component for rating the function with the averaged infrasonic noise signal. The function for mapping may be a non-linear function. This function may be used for weighting an additional rating signal, especially the averaged infrasonic noise signal. The function argument may by the result of an arbitrary combination of the averaged infrasonic signal and the averaged infrasonic noise signal. Particularly, the argument may be the result of the division of the averaged infrasonic signal and the averaged infrasonic noise signal. Therefore, the module may comprise a dividing component for the averaged infrasonic signal and the averaged infrasonic noise signal. Moreover, the function may map the result the division of the averaged infrasonic signal and the averaged infrasonic noise signal to provide a function result and this function result may be multiplied with the averaged infrasonic noise signal to provide the infrasonic noise signal.
The offset value may be an absolute offset value, increasing the averaged infrasonic noise signal by a constant absolute value. The offset value may be a relative offset value. The increasing offset of the averaged infrasonic noise signal is determined relatively to the averaged infrasonic noise signal. Further, the offset value may be offset by multiplying with the averaged infrasonic noise signal to provide the infrasonic level signal. Particularly, the offset value may be defined by a signal-to-noise ratio (SNR). Moreover, the offset value may be adjustable to adapt the evaluation method to different operating conditions.
According to another aspect of the invention a device of a surveillance system for monitoring by evaluating an infrasonic signal is provided. The device comprises a detector to detect sound waves, a processing unit and components responsive to a trigger signal. The detector is adapted to a sound wave frequency range including an infrasonic frequency range. The processing unit executes the operation of the aforementioned method of a surveillance system for monitoring by evaluating an infrasonic signal and the infrasonic signal is provided by the detector. The trigger signal is generated according to the aforementioned method and initiates operations and functions of the device. The detector signals may have to be filtered to extract infrasonic signals out of the detector signals.
The detector for detecting infrasonic signals may be a microphone. The microphone may be adapted to an infrasonic frequency range. Further, the microphone may be adapted to an infrasonic frequency range and a frequency range of audio signals occurring in voice or speech.
The device may be a mobile phone. The mobile phone may be a mobile phone built-in a motor vehicle. Mobile phones include digital signal processing units to operate on voice signals of the user. These digital processing units may also operate the evaluation of the infrasonic signals. Therefore, it may be necessary that each mobile phones provide microphones which are able to detect both infrasonic signals and voice/speech signals.
The device may be a voice/speech controlled device. Device functions of such devices may be controlled by spoken commands. Therefore, the devices may each comprise a voice signal processing unit. This voice signal processing unit may also operate the evaluation of the infrasonic signals. Therefore, it may be necessary that the devices include microphones which are able to detect both infrasonic signals and voice/speech signals.
According to another aspect of the invention a system of a surveillance system for monitoring by evaluating an infrasonic signal is provided. The system comprises a module according to the aforementioned module of a surveillance system for monitoring by evaluating an infrasonic signal and a device processing voice/speech signals and infrasonic signals. This device comprises a detector to detect sound waves and components responsive to a trigger signal. The detector is adapted to a sound wave frequency range including an infrasonic frequency range. The trigger signal is provided by the module. The detector signals may have to be filtered to extract infrasonic signals out of the detector signals.
The detector for detecting infrasonic signals may be a microphone. The microphone may be adapted to an infrasonic frequency range. Further, the microphone may be adapted to an infrasonic frequency range and a frequency range of audio signals occurring in voice or speech sound signals.
The device may be a voice/speech controlled device. Device functions of such devices may be controlled by spoken commands. Therefore, the devices may each comprise a voice signal processing unit. This voice signal processing unit may also operate the evaluation of the infrasonic signals. Therefore, it may be necessary that the devices include microphones which are able to detect both infrasonic signals and voice/speech signals.